Alternating current/direct current (AC/DC) converters may be used in AC/DC power supplies to operate electrical devices that operate on direct current, and AC/DC converter may use large capacity block condensers or the like to convert alternating current into direct current. When the supply of power from the AC/DC power supply is interrupted due to power failures, etc., power may still supplied to receiving electrical devices from the AC/DC power supply for a certain amount of time due to the energy accumulated in the block condensers or similar. To enable a device shutdown processing or an operational shutdown of the electrical devices receiving the power, the AC/DC converter may output a detection signal to the respective electrical devices when an interruption in the supply of power from the AC/DC power supply is detected. In response to this detection signal, the electrical devices may execute the shutdown processing during a period until the power supplied from the AC/DC converter completely stops. The faster the AC/DC converter detects the interruption of the power supply, the sooner the shutdown processing may begin, which reduces time that the AC/DC converter has to continue to supply power. As the time that the power has to be supplied decreases, the capacity of the of the block condensers or similar may be reduced, and so it is desirable to quickly detect interruptions in the supply of alternating current power.
A power supply device has been proposed to detect the supply interruption of the alternating current power supply by generating a pulsating current is generated with full-wave rectification of the alternating current, for example, and then comparing the voltage of the pulsating current with a reference voltage derived from dividing the peak voltage of this pulsating current (refer to Japanese Unexamined Patent Application Publication No. 2010-261862). This power supply device detects an interruption in the supply of alternating current when a state in which the pulsating current voltage is higher than the reference voltage for a time longer than a timeout time, or when a state in which the pulsating current voltage at or below the reference voltage for a time longer than a timeout time.